1. Field of the Invention
The present invention relates to a line switching system, an optical transmission switching device, a multiplex system and an Ethernet redundant method and the system, which are best applicable to a multiplex communication, specifically, to communication using Ethernet®.
2. Description of the Related Art
When achieving the multiplex communication, a line switching system is employed in which a plurality of lines are provided within the communication system and switching of the line (communication path) to be used is performed when, for example, a communication fault is generated in some part of the line.
As an example of a conventional data transmission system, there is a system comprising, in order to improve the reliability of the transmission, a present system line which is regularly used for communication and the standby system line, in which the line is switched to be used for the communication.
For example, a transmission system using Ether frame is less expensive compared to SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy) and has been largely used for LAN. The capacity of the transmission suing the Ether frame has been increased to meet the need of the times and the transmission capacity by one line has been rapidly increasing. Generation of a fault in such interface means interrupting a large amount of data so that the damage is enormous. In a network built by using a router, in general, there is a method in which the transmission path is switched by using a routing protocol when there is a fault.
A wavelength multiplex optical communication system disclosed in Japanese Patent Application Laid-open No. 11-50551 applied earlier by the applicant of this application comprises: as a present optical transmission system and a standby optical transmission system, an optical transmission system, respectively, in which a wavelength multiplex optical communication device having a transmission part and a reception part of wavelength multiplex signal light is placed through an optical transmission line. The reception part of the wavelength multiplex optical communication device comprises an alarm circuit for outputting an alarm signal when the signal light is not normally received, and an attenuator for attenuating the wavelength multiplex signal light when receiving the alarm signal outputted from the alarm circuit.
Thereby, all the light signals which are wavelength-multiplexed are automatically switched to the other transmission path so that it is possible to achieve maintenance and restoration work more rapidly compared to that of the related art.
However, in the above-described conventional system in which the transmission path is switched using the routing protocol, it requires rerouting of the lines to the other line by a router or the like. Thus, it takes an incredibly longer time from the detection of a fault to the completion of switching compared to a duplex switching by a protocol with a function of switching the lines such as SONET/SDH. Therefore, an enormous amount of notification is o be lost during the time.
If there is a switching system as that in SONET/SDH to be applied at the point of transmitting the Ether frame, however, there is no such system in the standard of Ethernet®. That is, in the case of achieving communication using a protocol without the function of switching the lines, it is time-consuming to perform duplex switching. Further, if a new protocol is provided to achieve this, it becomes incompatible in regards to interface.
A subject has been raised on how to achieve duplication of the line in the interface having no duplex switching protocol without changing a basic protocol in a network device. By defining a new protocol and terminating at a switching point, the interface becomes incompatible and the specification needs to be changed by each device. Further, by terminating the protocol, the device becomes complicated thereby increasing the price.
Further, the wavelength multiplex optical communication system disclosed in Japanese Patent Application No. 11-150511 utilizes the line-switching function of the protocol so that it is not applicable to the protocol with no line-switching function.
Furthermore, conventionally, there are also problems in regards to an optical transmission switching device, a multiplex system, and Ethernet system, respectively, used in a multiplex communication.